Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research

Performance of a high sensitivity multi-element tissue equivalent proportional counter for radiation protection neutron monitoring measurements

This study describes the performance of a novel design of compact multi-element tissue equivalent proportional counter (METEPC), which consists of 61 individual cylindrical counting volumes machined in a single block of tissue equivalent plastic. Each counting volume is a separate cylinder of internal diameter of 0.5 cm and height 5 cm. The performance of the METEPC was examined experimentally to obtain microdosimetric information, absorbed dose, dose equivalent, and sensitivity in the neutron energy range of 34 to 423 keV where commercially available tissue equivalent proportional counters (TEPCs) under respond as much as 40% of the ambient dose equivalent. A simple elongated cylindrical sampling geometry of METEPC provides very good estimates of microdosimetric average, y(D), and dosimetric quantities of interest, H*(10) and Q, which are comparable to those obtained with the conventional spherical sampling geometry of a standard TEPC. The sensitivity of METEPC is comparable to that of a conventional 12.7 cm diameter TEPC, which suggests that it is able to produce measurements in low dose rate radiation environments with the same precision in a given length of time as that obtained with the conventional TEPC. METEPC, being possibly the simplest design available in the multi-element geometrical configuration and approximately 9 times smaller in volume than that of a conventional 12.7 cm diameter TEPC, could form the basis of a portable monitoring system in mixed field radiation environments and may also be useful for radiation dosimetric measurements in beams of limited cross-sections and in phantoms.

Relative biological effectiveness of 280 keV neutrons for apoptosis in human lymphocytes

The relative biological effectiveness (RBE) of neutrons varies from unity to greater than ten depending upon neutron energy and the biological endpoint measured. In our study, we examined apoptosis in human lymphocytes to assess the RBE of low energy 280 keV neutrons compared to Cs gamma radiation and found the RBE to be approximately one. Similar results have been observed for high energy neutrons using the same endpoint. As apoptosis is a major process that influences the consequences of radiation exposure, our results indicate that biological effect and the corresponding weighting factors for 280 keV neutrons may be lower in some cell types and tissues.

A Dose Threshold for a Medium Transfer Bystander Effect for a Human Skin Cell Line

The existence of radiation-induced bystander effects mediated by diffusible factors is now accepted, but the mechanisms and precise behavior at low doses remain unclear. We exposed cells to gamma-ray doses in the range 0.04 mGy-5 Gy, harvested the culture medium, and transferred it to unirradiated reporter cells. Calcium fluxes and clonogenic survival were measured in the recipients. We show evidence for a dose threshold around 2 mGy for the human skin cell line used with a suggestion of increased survival below that dose. Similar experiments using direct gamma irradiation showed no reduction in survival until the dose exceeded 7 mGy. Preliminary data for neutrons where the gamma-ray dose was kept below the bystander threshold do not show a significant bystander effect in the dose range 1-33 mGy. A lack of a bystander response with neutrons occurred at around 1 Gy, where significant cell killing from direct irradiation was observed. The result may have implications for understanding the role of bystander effects at low doses.

Monte Carlo simulation of neutron irradiation facility developed for accelerator based in vivo neutron activation measurements in human hand bones

The neutron irradiation facility developed at the McMaster University 3 MV Van de Graaff accelerator was employed to assess in vivo elemental content of aluminum and manganese in human hands. These measurements were carried out to monitor the long-term exposure of these potentially toxic trace elements through hand bone levels. The dose equivalent delivered to a patient during irradiation procedure is the limiting factor for IVNAA measurements. This article describes a method to estimate the average radiation dose equivalent delivered to the patient's hand during irradiation. The computational method described in this work augments the dose measurements carried out earlier [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724]. This method employs the Monte Carlo simulation of hand irradiation facility using MCNP4B. Based on the estimated dose equivalents received by the patient hand, the proposed irradiation procedure for the IVNAA measurement of manganese in human hands [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724] with normal (1 ppm) and elevated manganese content can be carried out with a reasonably low dose of 31 mSv to the hand. Sixty-three percent of the total dose equivalent is delivered by non-useful fast group (> 10 keV); the filtration of this neutron group from the beam will further decrease the dose equivalent to the patient's hand.